Chondrosarcoma of Iliac Bone Imaging Spectrum With Histopathological Correlation: A Case Report

Chondrosarcoma is a rare form of carcinoma that originates in the cells of cartilage, the flexible tissue that cushions the joints and gives structure to various parts of the body. This malignant tumour primarily affects adults and is most commonly found in the bones of the arms, legs, pelvis, and ribs. The severity and prognosis of chondrosarcoma can vary widely depending on factors such as tumour size, location, and grade. We are reporting a case of an 83-year-old male patient who presented with swelling over the left hip joint. A mass was detected on radiograph and ultrasound that was further characterized using contrast-enhanced CT and MRI. Imaging findings suggested chondrosarcoma. The patient was diagnosed on histopathological examination.


Introduction
Chondrosarcomas comprise around 10-15% of malignant bone tumours, exhibiting slow growth and a higher occurrence in regions like the femur, humerus, pelvis, scapula, and ribs [1].More uncommon sites encompass the neck and craniofacial area.Within bone locations, chondrosarcomas are typically categorized into two groups: those originating from the central or medullary cavity and those emerging from the bone's surface, termed peripheral or juxtacortical chondrosarcomas.While the majority of chondrosarcomas originate centrally and are primary, some can be secondary, stemming from an osteochondroma or enchondroma.These tumours predominantly manifest in adulthood or later stages of life, with a higher incidence in males.Clinical presentations commonly involve pain and swelling.Pathological classification of chondrosarcomas includes conventional and nonconventional subtypes, such as dedifferentiated, mesenchymal, clear cell, and extraskeletal myxoid variations [1].

Case Presentation
An 83-year-old male patient presented with swelling over the left hip and restricted joint movement in the last six months.The swelling was associated with pain.There was no history of trauma.On local examination, the swelling was soft, non-tender, and firm in consistency measuring 10 x 14 cm.No local rise in temperature or discolouration was noted.
On plain radiograph, an ill-defined, large lobulated soft tissue density lesion with permeative bone destruction was seen.Calcific foci were noted within it giving a heterogenous appearance suggestive of matrix mineralisation (Figure 1).On CT, an ill-defined soft tissue mass measuring 18 x 13.2 x 11.5 cm encased the iliac blade on the left side, extending from the left hip to the left paraspinal muscles.There was a mixture of hyperdense and hypodense areas noted reflecting the heterogeneous nature of the tumour.Central and peripheral calcifications were noted within the tumour (Figure 3).MRI revealed altered signal intensity in an 18.7 x 12.4 x 13.8 cm lesion within the left hip subcutaneous layer, extending to the para-spinal space.It appeared iso-hypointense on T1WI, mostly hyperintense on T2WI (Figure 4).It appeared hyperintense on short tau inversion recovery (STIR) with cystic spaces within (Figure 5).It shows restricted diffusion on diffusion-weighted imaging (Figure 6).It showed heterogeneous enhancement, the lesion encased the left iliac blade causing bone destruction (Figure 7).On the Time Resolved Imaging of Contrast Kinetics (TRICKS) angio sequence, the lesion is seen to be displacing the common, external and internal iliac artery towards the right side; however, no invasion is noted (Figure 8).

TRICKS: Time Resolved Imaging of Contrast Kinetics
The patient underwent fine needle aspiration cytology (FNAC), which revealed clusters of monomorphic cells and a few scattered large cells.The cells were bland with abundant eosinophilic and vacuolated cytoplasm.Few cells showed mild anisonucleiosis and binucleation.The background showed myxoid material; however, mitosis and osteoclastic giant cells were not seen.It depicted low-grade chondrosarcoma (Figure 9).

Discussion
Chondrosarcoma, a malignancy generating cartilage matrix, presents as primary (de novo) or secondary (superimposed on benign cartilaginous neoplasms).Categorized by osseous location, it encompasses central and peripheral types, the latter further divided into those arising from a preexisting osteochondroma and those developing on the bone surface (juxtacortical) [2].In descending order of occurrence, central chondrosarcomas are commonly found in the proximal femur, iliac bone, pubic bone, sacrum, and ischial bone.In the case of peripheral chondrosarcomas, the frequency distribution is as follows: iliac bone, pubic bone and proximal femur.Moreover, these tumours possess high fragility, rendering them prone to breakage during surgical handling, thereby increasing the likelihood of tumour spillage within the surgical site.This, in turn, frequently leads to the occurrence of multiple soft tissue recurrences [3].
Conventional intramedullary chondrosarcoma, commonly termed central chondrosarcoma, constitutes the predominant primary subtype.Clinical manifestations are vague, with pain as the prevailing symptom in over 95% of cases.This pain, often gradual and worsening at night, persists for months to years prior to diagnosis.A palpable soft-tissue mass or swelling has been noted in 28-82% of individuals [2].
Plain films serve to depict and locate lesions, revealing their cartilaginous nature and aggressiveness.Central chondrosarcoma, the prevalent type, originates in the metaphysis and extends to the diaphysis.The lytic lesion displays well-defined characteristics, often with mixed lytic and sclerotic features, including characteristic ring-and-arc calcification patterns, endosteal scalloping, cortical changes, and irregular margins in high-grade cases.Calcifications within the tumour matrix vary in pattern, presence, and density.When invading soft tissue, the mass becomes palpable [4].Ultrasound doesn't have any specific role in bone tumours if the tumour is restricted to the intramedullary cavity and cortical destruction is absent.If the bone tumours are present with cortical destruction and involve adjacent soft tissue, colour Doppler gives an idea about soft tissue changes, cystic areas within, and vascularity.However, colour Doppler doesn't give a

FIGURE 1 :
FIGURE 1: An ill-defined lobulated mass (white arrows) with calcific foci (yellow arrow) on left side causing displacement of left hip joint towards medial side.

FIGURE 2 :
FIGURE 2: A large heterogeneous mass (white arrow) with flecks of calcification (red arrow) and cystic spaces (yellow arrow) noted within.

FIGURE 3 :
FIGURE 3: CT showing large large soft tissue mass encasing left iliac blade (white arrows).Few calcific foci are noted in central (yellow arrow) and periphery.

FIGURE 4 :FIGURE 5 :
FIGURE 4: (A) Coronal T1WI image showing large soft tissue mass (white arrow) encasing the left iliac blade appearing isointense; (B) On coronal T2WI image, same mass appears hyperintense with few cystic spaces

FIGURE 6 :
FIGURE 6: Diffusion-weighted imaging shows mild diffusion in the lesion site (white arrow).

FIGURE 7 :
FIGURE 7: On post-contrast imaging, heterogeneous central and peripheral enhancement is noted.

FIGURE 8 :
FIGURE 8: On TRICKS angio sequence, the lesion is seen to be displacing the common, external, and internal iliac artery towards the right side; however, no invasion is noted.

FIGURE 9 :
FIGURE 9: Clusters of monomorphic cells and few scattered large cells with abundant eosinophilic cytoplasm.Background shows myxoid material.